1. Field of Invention
The invention relates generally to vacuum operated valves and more specifically to a time delay valve for controlling operation of an exhaust gas recirculation controller.
2. Description of the Prior Art
The use of exhaust gas recirculation (EGR) valves to reduce undesirable exhaust emissions in automotive internal combustion engines has become widespread. While many different valves are available, most are similar in the respect that they utilize a vacuum signal representative of air flow into the engine to actuate the valve to permit the recirculation of exhaust gases. This signal is typically either taken at the carburetor throttle valve whereat it is generally referred to as ported vacuum and transmitted directly to the EGR valve or at the carburetor venturi and amplified to a level sufficient to operate the EGR valve.
In either case a somewhat undesirable transient condition exists during and shortly after starting the engine in that the immediate application of a vacuum signal to the EGR valve from the carburetor throttle valve or venturi can result in the recirculation of exhaust gases during this time period. This recirculation tends to delay the stabilization of combustion and of engine operating temperature upon starting, thereby burdening the starting cycle and causing undue wear of engine components.
It is therefore considered advantageous to delay the operation of the EGR valve until after the start cycle is complete. In accomplishing this delay, however, it is desirable that the means employed to effect the delay be inoperative during normal engine operation. It is also desirable that this time delay for EGR valve operation during starting also be capable of rapid repetitive operation to accommodate quick restarting of an engine without actuation of the EGR valve.
To accomplish these desirable functions prior art exhaust gas recirculation systems have uneconomically employed relatively expensive engine condition transducers and solenoid operated valves.